Re: [PATCH v10 10/31] tools/libxl: add back channel support to write stream

[Wei Liu <wei.liu2@citrix.com>]

On Fri, Feb 26, 2016 at 10:11:27AM +0800, Wen Congyang wrote:
> On 02/25/2016 11:54 PM, Wei Liu wrote:
> > On Mon, Feb 22, 2016 at 10:52:14AM +0800, Wen Congyang wrote:
> >> Add back channel support to write stream. If the write stream is
> >> a back channel stream, this means the write stream is used by
> >> Secondary to send some records back.
> >>
> >> Signed-off-by: Yang Hongyang <hongyang.yang@easystack.cn>
> >> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
> >> ---
> >>  tools/libxl/libxl_dom_save.c     |  1 +
> >>  tools/libxl/libxl_internal.h     |  1 +
> >>  tools/libxl/libxl_stream_write.c | 26 ++++++++++++++++++++------
> >>  3 files changed, 22 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/tools/libxl/libxl_dom_save.c b/tools/libxl/libxl_dom_save.c
> >> index 72b61c7..18946c5 100644
> >> --- a/tools/libxl/libxl_dom_save.c
> >> +++ b/tools/libxl/libxl_dom_save.c
> >> @@ -404,6 +404,7 @@ void libxl__domain_save(libxl__egc *egc, libxl__domain_save_state *dss)
> >>      dss->sws.ao  = dss->ao;
> >>      dss->sws.dss = dss;
> >>      dss->sws.fd  = dss->fd;
> >> +    dss->sws.back_channel = false;
> >>      dss->sws.completion_callback = stream_done;
> >>  
> >>      libxl__stream_write_start(egc, &dss->sws);
> >> diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> >> index 3d3e8e8..e02e554 100644
> >> --- a/tools/libxl/libxl_internal.h
> >> +++ b/tools/libxl/libxl_internal.h
> >> @@ -3044,6 +3044,7 @@ struct libxl__stream_write_state {
> >>      libxl__ao *ao;
> >>      libxl__domain_save_state *dss;
> >>      int fd;
> >> +    bool back_channel;
> >>      void (*completion_callback)(libxl__egc *egc,
> >>                                  libxl__stream_write_state *sws,
> >>                                  int rc);
> >> diff --git a/tools/libxl/libxl_stream_write.c b/tools/libxl/libxl_stream_write.c
> >> index f6ea55d..5379126 100644
> >> --- a/tools/libxl/libxl_stream_write.c
> >> +++ b/tools/libxl/libxl_stream_write.c
> >> @@ -49,6 +49,13 @@
> >>   *  - if (hvm)
> >>   *      - Emulator context record
> >>   *  - Checkpoint end record
> >> + *
> >> + * For back channel stream:
> >> + * - libxl__stream_write_start()
> >> + *    - Set up the stream to running state
> >> + *
> >> + * - Add a new API to write the record. When the record is written
> >> + *   out, call stream->checkpoint_callback() to return.
> > 
> > What does this mean? Which new API?
> 
> The next patch introduces this API. The commits is very old.
> 
> I think I can merge these two patches into one patch.
> 

Please reference the actual function / API.

> > 
> >>   */
> >>  
> >>  /* Success/error/cleanup handling. */
> >> @@ -225,6 +232,15 @@ void libxl__stream_write_start(libxl__egc *egc,
> >>  
> >>      stream->running = true;
> >>  
> >> +    dc->ao        = ao;
> >> +    dc->readfd    = -1;
> >> +    dc->copywhat  = "save v2 stream";
> >> +    dc->writefd   = stream->fd;
> >> +    dc->maxsz     = -1;
> >> +
> >> +    if (stream->back_channel)
> >> +        return;
> >> +
> > 
> > There seems to be very subtle change of behaviour.
> > 
> > Before this patch, the dc->* are not set until the emulator check is
> > done. With this path, it is possible in the normal case some of the
> > fields are initialised in the error path.
> > 
> > I think this is OK given the callbacks in the upper layer and in
> > the writer don't rely on those fields to clean up. Just one thing to
> > note.
> > 
> > That said, I suggest you move all initialisation of dc->* in one place.
> 
> OK, I will do it.
> 
> > 
> >>      if (dss->type == LIBXL_DOMAIN_TYPE_HVM) {
> >>          stream->device_model_version =
> >>              libxl__device_model_version_running(gc, dss->domid);
> >> @@ -249,12 +265,7 @@ void libxl__stream_write_start(libxl__egc *egc,
> >>          stream->emu_sub_hdr.index = 0;
> >>      }
> >>  
> >> -    dc->ao        = ao;
> >> -    dc->readfd    = -1;
> >>      dc->writewhat = "stream header";
> >> -    dc->copywhat  = "save v2 stream";
> >> -    dc->writefd   = stream->fd;
> >> -    dc->maxsz     = -1;
> >>      dc->callback  = stream_header_done;
> >>  
> >>      rc = libxl__datacopier_start(dc);
> >> @@ -279,6 +290,7 @@ void libxl__stream_write_start_checkpoint(libxl__egc *egc,
> >>  {
> >>      assert(stream->running);
> >>      assert(!stream->in_checkpoint);
> >> +    assert(!stream->back_channel);
> >>      stream->in_checkpoint = true;
> >>  
> >>      write_emulator_xenstore_record(egc, stream);
> >> @@ -590,7 +602,9 @@ static void stream_done(libxl__egc *egc,
> >>          libxl__carefd_close(stream->emu_carefd);
> >>      free(stream->emu_body);
> >>  
> >> -    check_all_finished(egc, stream, rc);
> >> +    if (!stream->back_channel)
> >> +        /* back channel stream doesn't have save helper */
> >> +        check_all_finished(egc, stream, rc);
> > 
> > Though it doesn't have helper, do you not need to check if the back
> > channel stream itself is OK? The comment itself doesn't seem to justify
> > this change.
> 
> What do you want to check? assert(!stream->shs) or
> assert(!libxl__stream_write_inuse(stream))?


The stream itself is not in use.

Also check_all_finished calls completion_callback. Don't you need that,
too?

Wei.

> 
> Thanks
> Wen Congyang
> 
> > 
> > Wei.
> > 
> >>  }
> >>  
> >>  static void checkpoint_done(libxl__egc *egc,
> >> -- 
> >> 2.5.0
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@lists.xen.org
> >> http://lists.xen.org/xen-devel
> > 
> > 
> > .
> > 
> 
> 
> 

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